Methods are known in the prior art concerning copper hydrometallurgy which involve recovery of cuprous chloride from process solutions with subsequent reduction to produce and recover copper metal. Patents of this type include U.S. Pat. Nos. 3,798,026, 3,972,711, 4,039,324 and 4,013,457. Major work in this field may be found in U.S. Pat. Nos. 3,785,944 and 3,879,272 to Atwood et al which are concerned with hydrometallurgical processes for pollution free recovery of metallic copper from copper ores such as chalcopyrite, the most common copper-containing ore in the United States. U.S. Pat. No. 3,785,944 describes a basic hydrometallurgical process for processing copper sulfide ore concentrates, especially those containing chalcopyrite. This process has four basic stages: an oxidation stage in which copper-containing materials are oxidized with a solution containing ferric chloride and cupric chloride to form a solution containing ferrous chloride and cuprous chloride; a reduction stage in which any remaining cupric chloride in the solution from the oxidation stage is reduced to cuprous chloride, preferably by use of fresh cement copper; a copper recovery stage in which metallic copper is recovered from the cuprous chloride solution, preferably by electrolysis; and a regeneration-purge stage in which ferric chloride and cupric chloride are regenerated by oxidation with concurrent purge of excess iron as well as sulfate ions and other impurities. The resulting leach solution is then used to oxidize additional copper-containing ore.
U.S. Pat. No. 3,879,272 to the same inventors describe improvements on the process of U.S. Pat. No. 3,785,944, especially in combining the oxidation and regeneration-purge stage and use of KCl in the system. In these patents, the reduced leach solution or electrolyte which is subsequently electrolyzed, contains impurities which are electrolyzed with the copper and it is desirable that these impurities be removed prior to electrolysis.
U.S. Pat. No. 3,972,711 claims an improvement over the Atwood patents on the basis that because the reduced leach solution of Atwood contains certain impurities, improved results are obtained by crystallizing cuprous chloride from the system so as to produce a purer grade of copper. In this process, the cuprous chloride is crystallized in the presence of a specified amount of cupric chloride.
The present invention represents an improvement over the processes of the above-discussed patents in obtaining a purer grade of copper because the presence of impurities is minimized within the system prior to electrolysis by providing a crystallization stage wherein solids in the form of potassium chloride-cuprous chloride salts are crystallized and removed from the system to increase the purity of the resultant copper.
Complex salts of potassium chlorides and copper chloride are known in the art and have been reported in the literature by several authors. Species such as KCuCl.sub.2, K.sub.2 CuCl.sub.3 and KCuCl.sub.2.H.sub.2 O are reported by the following authors: J. J. P. Valeton and W. Fromel, Z. anorg. allgem. Chemie, 137, 91 (1924); O. A. Chaltykyan, Zhur. Obshchei Khim., 18, 1626 (1948); W. U. Malik, et al., Z. anorg. allgem. Chemie, 299 322 (1959). However, none of these complex salts are recovered and produced by crystallization from process streams of any type.